Chapter-Chapter 2: Understanding the Weather Social Science Part-1 class 7 in english Medium CBSE Notes

Quick Revision Notes – Understanding the Weather

Weather

• Weather is the condition of the atmosphere at a particular place and time.
• Weather changes from day to day.
• Most weather phenomena occur in the Troposphere, the lowest layer of the atmosphere.

Elements of Weather

• Temperature – How hot or cold the air is.
• Precipitation – Rain, snow, sleet, or hail falling from the sky.
• Atmospheric Pressure – The weight of air pressing on the Earth's surface.
• Wind – Movement of air from one place to another.
• Humidity – Amount of water vapour present in the air.

Traditional Weather Prediction

• People observed nature to predict weather.
• Ants carrying eggs to higher ground may indicate rain.
• Frogs croaking loudly often suggest rainfall.
• Pine cones close in humid weather and open in dry weather.

Temperature

• Temperature tells us how hot or cold the atmosphere is.
• Measured using a Thermometer.
• Common scales:
  • Celsius (°C)
  • Fahrenheit (°F)
• Digital thermometers provide more accurate readings.

Important Terms

• Maximum Temperature – Highest temperature of the day.
• Minimum Temperature – Lowest temperature of the day.
• Range of Temperature = Maximum Temperature − Minimum Temperature
• Mean Daily Temperature = (Maximum + Minimum) ÷ 2

Precipitation

• Includes rain, snow, sleet, and hail.
• Measured using a Rain Gauge.
• Rainfall is measured in millimetres (mm).
• If 5 mm water is collected, rainfall is recorded as 5 mm.

Atmospheric Pressure

• The pressure exerted by the weight of air.
• Measured using a Barometer.
• Unit: Millibar (mb).
• Normal atmospheric pressure at sea level is about 1013 mb.
• Pressure below 1000 mb may indicate a depression or storm.

Key Facts

• Pressure decreases with altitude.
• Mountain regions have lower atmospheric pressure.
• Low-pressure systems can develop into cyclones.

Wind

• Wind is the movement of air from high-pressure areas to low-pressure areas.
• Two important characteristics:
  • Direction
  • Speed

Instruments

• Wind Vane – Measures wind direction.
• Anemometer – Measures wind speed.

Importance of Wind

• Helps in weather forecasting.
• Important for farmers, sailors, and pilots.
• Helps in seed dispersal.

Humidity

• Humidity is the amount of water vapour present in the air.
• Measured using a Hygrometer.
• Expressed as Relative Humidity (%).

Humidity Levels

• Dry weather: 20% – 40%
• Humid weather: 60% – 80%
• Saturated air: 100%

Effects of Humidity

• High humidity slows evaporation.
• Wet clothes dry slowly in humid weather.
• People sweat more in humid conditions.

Weather Station

• A weather station contains instruments used to measure weather elements.
• Records temperature, rainfall, humidity, pressure, and wind.
• Helps scientists monitor and forecast weather.

Automated Weather Station (AWS)

• Works automatically without human intervention.
• Uses sensors to collect weather data.
• Provides accurate and timely information.
• Used in agriculture, aviation, navigation, and disaster management.

Predicting the Weather

• Scientists who study weather are called Meteorologists.
• The study of weather is called Meteorology.
• Weather forecasts help predict future weather conditions.

Importance of Weather Forecasts

• Warn people about cyclones, floods, and storms.
• Help farmers plan agricultural activities.
• Assist fishermen and sailors.
• Support disaster management efforts.
• Help governments prepare for emergencies.

Weather Instruments and Their Functions

Important Terms

• Weather: Condition of the atmosphere at a specific place and time.
• Meteorology: Scientific study of weather.
• Forecast: Prediction of future weather.
• Water Vapour: Water in gaseous form.
• Hail: Small balls of ice falling from clouds.
• Sleet: Frozen or partially frozen rain.
• Humidity: Amount of moisture in the air.

Exam Booster Facts

• Weather occurs mainly in the Troposphere.
• Rainfall is measured in millimetres (mm).
• Normal sea-level pressure is 1013 mb.
• Wind moves from high pressure to low pressure.
• Humidity is measured by a Hygrometer.
• Wind speed is measured by an Anemometer.
• Rainfall is measured by a Rain Gauge.
• Atmospheric pressure is measured by a Barometer.
• The study of weather is called Meteorology.
• Weather forecasts help reduce disaster risks.